Farm Environment During Pregnancy and Childhood and Polysensitization at the Age of 31: Prospective Birth Cohort Study in Finland

The farm environment, especially contact with farm animals in early childhood, may prevent allergic sensitization during adulthood. However, prospective associations between exposure to the farm environment and polysensitization have not been studied. Polysensitization is a risk factor for asthma and asthma-related morbidity. Objective: To investigate whether exposure to a farming environment in early childhood, especially exposure to animals, is associated with sensitization to specific allergens and polysensitization at the age of 31. In a prospective birth cohort study, 5509 individuals born in northern Finland in 1966 underwent skin prick testing against birch, timothy, cat, and house dust mite at the age of 31. Prenatal exposure to the farming environment was documented at birth, whereas information on childhood exposure to pets was only collected retrospectively at the age of 31. Data were analyzed using logistic regression. Being born to a family with farm animals was associated with a reduced risk of sensitization to birch, timothy, and cat (adjusted odds ratio [aOR], 0.55 [95%CI, 0.43-0.70]; aOR, 0.62 [95%CI, 0.48-0.79]; aOR, 0.60 [95%CI, 0.47-0.75]) and polysensitization at the age of 31 (aOR, 0.62 [95%CI, 0.48-0.80]). The number of animal species present during childhood was dose-dependently associated with a reduced risk of sensitization to birch, timothy, and cat, as well as of polysensitization. No association was found with sensitization to house dust mite. Growing up on a farm and contact with higher numbers of animal species in childhood are associated with less frequent sensitization to birch, timothy, and cat allergens and polysensitization in adulthood, but not with sensitization to house dust mite.